Metbtob amd apparatus



R. A. FESSENDEN AND F. H. LESLIE.

Fv'EHOD AND APPARATUS FOR ELIMINATING UNDESIESD WBRATIONS.

APPLICATION HLED :UNE u. |911.

REGIN'LB FESSENDEN, 0F BROOKLIN'E, AND FREELANID H. LESLIE, 0F MILTON,

MASSACHUSETTS, ASSIGNORS T0 MAINE, A CORPORATION 0F MAINE.

SUBMARINE SIGNAL COMPANY, OF PURTLAND,

METEO@ AND APPRATUS FOR ELIMINATING UNDESIRED VIBRA'I'IONS.

Specification of Letters Patent.

Patented 60ct.. 21, 1919..

Application filed .Tune 8, 1917. Serial No. 173,614.

To all whom #may concern:

e it known that we, REGINALD A. FEssEN- Dinv, of Brookline, in the county of Norfolk and State of Massachusetts, and FREELAND H. LESLIE, of Milton, in said county and State, citizens of the United States, have invented a new and useful improvement in Methods and Apparatus for Eliminating of which the following is a specification. i

Our invention relates to vibratory bodies, and more especially to sound-producing bodies, and still more especially to bodies Vibrating at their natural frequencies, such ai diaphragms, tuning forks, rods and the li e.

llt has for its object the suppression to any desired extent of such vibration .fre-` quencies as are not desired, thereby broadly increasing the eciency of the generation and utilization of vibratory motion.

lin the accompanying drawings, forming a part of this specification, Figures land 2 are diagrams illustrative of the theory of our method, and l,

lFigs. 3 and i show diagrammatically formsof apparatus for carrying out our invention.

1t is well known in the art that vibratory bodies tend to vibrate at certain definite frequencies, which are called their natural periods.

F or example, a telephone diaphragm tends to vibrate at a period in the neighborhood of 1000 and a submarine oscillator diaphragm, of tipe type shown in United States Letters Patent No.`l,167,366 granted to said Fessenden January 4, 1916, as at present constructed, tends to vibrate at frequencies of 5110 and 1100, approximately.

The presence of these natural vibrations is frequently very objectionable. For example, in the telephone they unduly strengthen the higher tones of the voice though still permitting speech.

in the submarine oscillator they are so strong, however, that they do not transmit articulate speech at all. `When diaphragms are used for engine indicators, as by Perrys method, the natural Iperiod of the diaphragm tends to give incorrect indicator cards. iVhere a diaphragm is used to analyze sounds the overtones of the diaphragm make the research one of great diiiiculty. as

, sz'cal SoU/nds, lecture 5.

may be seen from Millers Scz'ence of Mu- Similar remarks apply to the notes of the diaphragm on phonograph records.

rThe applicants have discovered a method by which these undesirable harmonics may be eliminated, or reduced to any desired degree. rlllhe theory is illustrated in Fig. 1,

where 19 is the axis of the ordinates; 11, 12,

13, 14, 15 is the curve showing the relation mainingintensity will be uniform for alll frequencies, as shown in Fig. 2, where the strip 18 shows the intensity left after subtracting the figures' 16 and 17 from the original curve.

rihe applicants have discovered that these figures 16 and 17 correspond approximately lto the absorption humps of electrical resonant circuits and that by properly proportioning the self-induction, resistance and capacity in such a circuit, the amount of sound absorbed. can be made to correspond quite closely with any desired figure, as for example, 16 or 17, and the diaphragm thus made to vibrate substantially correctly over the entire range of frequencies. Fig. 3 shows such an arrangement as actually used for submarine telephony, which the applicants have accomplished up to a distance of five miles with clear and sharp articulation, whereas before only indistinct sounds could be observed, and thus for the first time it is possible for human beings to talk to one an other from one submarine to another through .the water there being two absorption circuits 23, 24: and 25 producing the absorption hump 16 and also 26, 27 and 28 producing the absorption hump 17.

ln Fig. 3, 21 is a telephone transmitter, here shown of' the ordinary type with battery 40, though any of the Well known amplifying devices known in the art may be used with it where more power is desired. 20 and 30 are wires leading from the transmitter to the oscillator 22.

On whistling into the transmitter 21 at 'different frequencies, commencing with a frequency of about 200 and gradually increasing to a frequency of about 1500, a curve of a character such as is shown at 11, 12, 13, 14, 15 in Fig. 1 will be obtained on plotting the resulting intensities. If the transmitter 21 be spoken into, with this strongly resonant type of diaphragm attached to the oscillator, only inarticulate soundsl will be heard. If, however, two shunted circuits are placed across the leads 29, 30, for example the circuit containing the inductance 23, resistance 24' and capacity 25, and also the circuit containing the inductance 2G, resistance 27 and capacity 28, these self inductances, resistances and capacities heilig suitably proportioned, the distortion may be entirely cured, and on now whistling into the transmitter 21 at different frequen-v cies, a substantially even curve, as shown in Fig. 2, will be obtained for the relation between frequency and intensity.

On talking into the transmitter 2l speech will now be emitted b the oscillator 22 very clearly and very distinctly.

We have taken as an illustration a diaphragm having its oscillator strongly resonant at two points, owing to its construction, but the same general system may be applied whether the number of resonant points be one or ten.

In Fig. 4 is shown this invention applied to a vibrating shaft.

31 is the pedestal; 32 the shaft; 33, 34, 35 are bearings; 39, 38 are piston rods running on eccentrics 36, 37 placed on the shaft as shown. 44 and 45 are cylinders open at the lower end; 40, 41 are pistons attached to the piston lrods 39, 38; and 43, 42 are holes in the piston for permitting air to escape into and, out of the cylinders 44 and 45 as the pistons 40 and 41 move up and down.

The applicants have found that the part of the shaft between the bearing 34, 35 may be considered, for mathematical purposes, as an electric circuit; the mass of the shaft corresponding to electric inertia, that is, self induction, the elasticity of the shaft corresponding to the reciprocal of electrical elasticity, that is, capaclty, and the friction of the shaft corresponding to the ohmic resistance.

Similarly, the portion of the shaft between the bearing 33, 34 may be mathematically considered as another electric circuit.

And these two mathematically-considercd electric circuits may be considered as coupled together electrically, the extent depending upon the rigidity of the bearing 34.

For example, if the bearing 34 fits so tightly that a vibration made by bending and suddenly releasing the shaft between the bearings 34, 35 is transmitted in a very slight degree to the portion of the shaft between the bearings 33, 34, then the coupling is considered to be what isdmown electrically asa loose coupling and the extent of the tightness of the coupling may be determined by measuring the extent to which the vibration of definite amount passes from t-he portion of the shaft between the bearings 34, 35 to the portion between the bearings 33, 34.

From this data a set of equations may be written down, similar to the well known equations for electrically-coupled circuits,

and from them the various modes of vibrations of the shaft at different frequencies, the different. resonance points and the amount of resonance may be calculated.

Having thus, or experimentally, determined the amount of resonance at digerent frequencies, if it is desired to eliminate that resonance, the size of the cylinders 44, 45 and the stroke of the eccentrics 3G, 37, and the size of the air-throttling passages 43, 42 and the mass of the pistons and piston rods 40, 39, 41, 38 are so determined that, just as in Fig. 1, the amount of power absorbed by the thr'ottling of the air through the air pistons 43, 42 is just sufficient to absorb the undesired resonant energy so that the shaft runs Without any strongly marked resonant frequency.

1n the electrical case shown in Fig. 3, the applicants have found that the inductance for the 540 period should be about 7 millihenries and for the 1200 frequency about 2 millihenries, and that the capacity for the 540 period should be about 10 microfarads and the capacity for the 1200 period about 2 microfarads, the resistance in each case being approximately'l ohm.

It is well known to those skilled in the art that in place of using absorbing circuits placed in shunt across the electric circuit, other equivalent means may be used.

What We claim is l. The method of eliminating undesired vibrations from a vibrating element, which consists in operatively connecting to the vibrating element a second vibratory energy-absorbing element, adjusting the frequency-determining constants of said second vibratory element so that the frequency of saidv second vibratory element is substan- Itially the same as the frequency of the undesired vibrations of the first vibrating element which it is desired to eliminate, and adjusting the frictional energy-absorbing constant of said second vibratory element so that the difference between the energy absorbed for a given frequency by the second vibratory element and the enerfry generated for said frequency by the rst Vibrating element will be equal in amount to the amount of vibration desired at said frequency.

- 2. The method of eliminating undesired vibrations from a vibrating element, which consists in operatively connecting to the vibrating element a second Vibratory energy-absorbing element, adjusting the frequency-determining constants of said second vibratory element so that the frequency of said second vibratory element is substantially the same asthe frequency of the undesired .vibrations of the first vibrating element which itis desired to eliminate, and adjusting 'the frictional energy-absorbing constant of said second Vibratory element so that the difference between the energy absorbed for a given frequency by the second vi'bratory element and the energy generated for said frequency by the first Vibrating element will be substantially equal in amount for all frequencies in the neighborhood of the undesired frequency.

REGINALD A. FESSENDEN. FREELAND H. LESLIE. 

